Help! He won't stay latched on!

Xav is already 6 months in 3 days and this is the first time I've encountered this kind of problem. To give you a little background on our feeding routine now - Xav is bottle-fed with my expressed breastmilk and NAN HA One formula during the day, then I would consistently nurse him at night before he sleeps. I still religiously pump at work and in the middle of the night but my milk supply can't keep up with my baby's increasing appetite. Just a week ago we've also started introducing rice cereals (Cerelac) but we only feed him with that once everyday.

So everything was running smoothly until the last two nights I wasn't able to nurse him directly before he sleeps. One night he was already too sleepy and the other night he was too full with formula milk. I think. Normally he would just look for my breast as he couldn't fall asleep without directly nursing at me! Until yesterday he just won't latch at all. He would even pull away and squirm! It was really frustrating! I felt that my baby either doesn't know me anymore or he has outgrown the need of latching on me. I tried doing it again upon waking up hungry this morning but no luck, still the same. He still pulls away after a few seconds. I gave him my BM in bottle and he was able to finish it so I'm guessing it's not the taste of my milk. I did a little research and found out it's called the "Nursing Strike".

Here are the things I saw on the net about Nursing Strike: 

Source: http://www.whattoexpect.com/first-year/week-21/nursing-strike.aspx

• Reacting to something you ate. If you recently indulged in a lot of spicy or strong-flavored food, the taste of your milk will change — maybe not for the better, according to your baby. Try cutting such foods from your diet to determine his dislikes, then avoid them until your baby has weaned.
• …or to a hormonal change. If you've been cutting down on nursings as your baby begins to eat more solid food, there's a chance that your periods could be returning (or you could be pregnant, gulp!). Either way, changes in your hormones can change the taste of your milk.
• Suffering from a stuffy nose. If he has a cold, plugged nostrils may force your baby to choose between nursing and breathing! Try saline drops and gentle suction with an aspirator to clear his nose (at least long enough for a meal).
• In pain. The sucking movements of nursing can intensify the pain of both teething and earaches. (If a tiny tooth is to blame, your baby will likely begin nursing with gusto, but then stop quickly as his gums begin to ache.) Check with your doctor about pain medications and other signs of an ear infection.
• Having a brush with thrush. This fungal infection is most common in newborns, but can occur in an older baby if he's taking antibiotics. Check for white patches on his tongue and in his mouth that reveal raw, sometimes bloody areas when you try to wipe them away. (Ouch! No wonder he doesn't want to nurse.) See your doctor — you'll bothneed to be treated so that you don't pass the infection back and forth (from his mouth to your nipples and vice versa).
• Simply impatient. If your letdown is slow, your eager eater may turn away from the breast in frustration — he wants his milk now, not in a minute or two or five when it starts flowing in earnest. Try pumping for a few minutes in advance of your nursing session, so that your baby isn't let down by that sluggish letdown.

By the way, the second bullet is very striking for me!!! I'm still trying to identify the real reason for this but I'm guessing it can be the slow letdown of my milk. 

Has anyone encountered this problem before? I'm sure it's not because of a stuffy nose, any pain or fungal infection. He really seems normal to me. Is it time to move on?

H-E-L-P! I still want to nurse him at night!